EP2252567B1 - Method and device for thermal partial oxidation of hydrocarbons - Google Patents

Description

The present invention relates to an improved process for the partial oxidation of hydrocarbons in a reactor, in which the reactor a hydrocarbon-containing stream and a stream containing oxygen is fed and an apparatus for performing the method according to the invention.

High-temperature reactions for the partial oxidation of hydrocarbons are usually carried out in a reactor system comprising mixing unit, burner and quench.

As an example of such a partial oxidation in the high temperature range, the production of acetylene and synthesis gas by partial oxidation of hydrocarbons may be mentioned. This is for example in DE 875198 . DE 1051845 . DE1057094 and DE 4422815 described.

Herein, the mixers / burners / furnace / quench combinations commonly used for the BASF Sachsse-Barthotomé acetylene process - hereinafter referred to as the combination, simply referred to as "reactor" - are explained.

The raw materials natural gas and oxygen are heated separately, usually as far as possible to 700 ° C. In a mixing zone, the reactants are mixed intensively and reacted after flowing through a burner block. The burner block in these cases consists of a certain number of parallel channels in which the flow velocity of the ignitable oxygen / gas mixture is higher than the flame speed (reaction rate, reaction rate) to prevent the flame from penetrating into the mixing chamber. The metallic burner block is cooled to withstand the thermal stresses. Depending on the time spent in the mixing room, there is a risk of flashback and ignition due to the limited thermal stability of the mixtures. Here, the term of the ignition delay time or induction time is used as the period in which an ignitable mixture undergoes no appreciable intrinsic thermal change. The induction time depends on the type of hydrocarbons used, the state of mixing, pressure and temperature. It determines the maximum residence time of the reactants in the mixing room. Reactants such as hydrogen, liquid gas or mineral spirits, whose use is particularly desirable due to yield and / or capacity increases in the synthesis process, are characterized by a comparatively high reactivity and thus low induction time.

The acetylene burners used in today's production scale are characterized by their cylindrical geometry of the combustion chamber (reactor). The burner block preferably has hexagonally arranged feedthrough bores. In one embodiment, e.g. 127 bores of 27 mm internal diameter arranged hexagonally on a circular base cross-section with a diameter of approx. 500 mm. As a rule, the channel diameters used are approximately 19 to 27 mm in diameter. The subsequent furnace, in which the flame of the acetylene-forming partial oxidation reaction is stabilized, is also of cylindrical cross-section and has the appearance of a short tube (of, for example, 533 mm diameter and 400 mm length). The entire burner of burner block and combustion chamber is suspended in a quench of larger cross-section via a flange from above. At the level of the exit plane from the furnace, quench nozzles are installed on one or more quench manifolds outside the circumference of the quench medium, which contain the quench medium, e.g. Atomize water or oil, with or without the aid of a sputtering medium and inject approximately perpendicular to the main flow direction of the combustion chamber leaving the reaction gases. This direct quench has the task of cooling the reacting flow extremely rapidly so that subsequent reactions, i. in particular the degradation of formed acetylene, be frozen. The range and distribution of the quenching beams is ideally dimensioned so that the most homogeneous possible temperature distribution is achieved in the shortest possible time.

The acetylene burners used in the current production scale are characterized by a cylindrical geometry of the combustion chamber. The feedstocks are premixed via a diffuser and fed to the burner block via hexagonally arranged feedthrough holes while avoiding backmixing. In the known processes, the premixing of the starting materials in the mixing diffuser takes place in a relatively large volume and under high preheating temperatures. Depending on the capacity of the burner, the mixing diffuser is characterized by a design in which the residence time of the reactants and their induction times are of the same order of magnitude. Due to an increased proportion of reactive feedstock components, catalytically active particles and surfaces, e.g. Coke, rust, etc., it may happen that the induction times for the ignition of the mixture are exceeded. These pre-ignition leads to business interruptions and thus to a reduction of the effectiveness and efficiency of the process.

In DE 10 2005 018 981 A1 or US 2,179,378 describes devices which move the introduction of the Reaktandenströme in a small space in the immediate vicinity of Brennerblockbohrungen. The burner block bores thus serve as mixing tubes in which the reactant mixture is formed. By a suitable design of the interference geometry high speeds are created, which prevent flashback of the flame into the burner block bores while ensuring rapid mixture formation.

In the DE-A 4422815 discloses a process for the production of acetylene and synthesis gas in which the channels of the burner block are covered on the upstream side of perforated plates (claim 1).

The implementation of this concept is associated with considerable design effort, since a uniform distribution of the reactant streams must be ensured distributed in suitable mixing units over all Brennererblockbohrungen. Furthermore, there is a risk of flashback in the individual mixing tubes and the stabilization of the flame in the stoichiometric range of the mixture field. This applies to the case of an unequal distribution of the reaction mixture, in which the flow velocity in the mixing tube decreases in the order of magnitude of the reaction rate.

The object was to find an improved process for the partial oxidation of hydrocarbons, which avoids the disadvantages mentioned and which allows in a simple process manner a fast and good mixing of the reactants in a very small space and short residence times.

Accordingly, a process for the partial oxidation of hydrocarbons has been found in a reactor in which the reactor a hydrocarbon-containing stream and an oxygen-containing stream zuleitet, which is characterized in that the two streams fed to the reactor in the reactor separately by leads one or more spatially separate lines, these lines have turbulence generators in their interior, due to which a highly turbulent flow field is formed by the predetermined deflection of the flow direction downstream of these turbulence generators and the streams then mixed after exiting the lines in a mixing zone and then in a reaction zone are reacted.

In the method according to the invention, the reactant streams are guided spatially separated from each other into preferably parallel bores, in which the flow through turbulence generators as high as possible turbulence structure is impressed. In the wake of the turbulence generators, the mixture formation of oxidizer and fuel now occurs in the smallest possible space, the degree of mixing depending on the mixing length, the degree of turbulence and the direction of rotation of the turbulence generator in the bores. Immediately adjacent to the mixing zone is the reaction zone, which is stabilized by injecting pilot oxygen into the highly turbulent flow zone.

By this sequential arrangement of mixing and reaction space a simple flow guidance is maintained, which is advantageously not disturbed by further installations.

The method according to the invention offers the possibility of preventing interruptions in operation and downtimes caused by pre-ignition. Furthermore, there are opportunities for the proportional use of fuels with low induction times such as synthesis gas or higher hydrocarbons (for example, ethane, ethylene or vaporized liquid gases).

In the method according to the invention known as turbulence generators internals are used in the channels of the burner block. The turbulence generators are in this case designed in such a way that, when inserted, they obstruct essential parts of the channel cross-section and the gas flow inside the channels is conducted only through continuous bores contained in the turbulence generators. Here, the channel cross-section is understood to be the area available to the gas for the passage of the channel.

In the case of the burner block passages, which are usually formed with a circular cross-section, such a turbulence generator preferably has the shape of a cylinder whose diameter is dimensioned such that it comes to the above-mentioned obstruction for the gas flow at the peripheral edges of this cylindrical body in the installed state, since the Outer diameter of the cylinder corresponds approximately to the inner diameter of the channel and thus a flow through the gas is almost completely prevented at the maximum still present in a very small extent gap. The quality of the seal is determined here in particular by the cost of production and can be further increased by further measures known to those skilled in the art.

The height of the cylindrical body used here is usually in a range of 1 to 4 channel diameters, preferably 2 to 3 channel diameter. In general, it is recommended that the method according to the invention design the turbulence generators in their geometry in such a way that 20 to 100% of the length of the burner channel is essentially blocked according to the invention.

The inventively introduced into the turbulence generator holes in the installed state substantially not or preferably not parallel to the longitudinal axis of the burner channel. In a preferred embodiment, in the case of the cylindrical body described above, this is provided with bores with a pitch angle of 80 ° to 40 °, preferably 60 ° to 45 °. The pitch angle is understood here as the angle between the longitudinal axis of the cylinder

(Height axis) and the longitudinal axis of the hole. In the case of axial alignment of the bores in the turbulence generator, this pitch angle would be 0 °. This bore is preferably attached to the upper or lower circular surface of the cylinder near or at the peripheral edge and then runs at a preferably constant pitch angle spirally to the opposite circular surface. It is recommended in this case to provide the turbulence generator with several holes, usually you choose here 1 to 6, preferably 4 holes.

In the installed state, the turbulence generators designed in this way cause the gas to necessarily flow through the bores. In this case, the gas flows due to the pitch angle of the holes in the form of the above-mentioned spiral movement. The direction of movement can therefore continue to be composed of a component in the direction of the longitudinal axis, on the other hand, however, this direction is also a peripheral component (depending on the location of the attached hole, for example, according to the circle formed by the diameter of the cylinder) superimposed. Until the gas has flowed through the entire turbulence generator, it experiences here an arcuate deflection in a circumferential angle of 45 ° to 360 °, preferably 90 ° to 180 °. The circumferential angle is understood to mean the swept over the entire section of the circular arc, which is given by the cylinder geometry. The deflection can be done both clockwise and counterclockwise.

According to the invention, a percentage area fraction of the channel cross section of 10% to 70%, preferably 20% to 50%, is blocked by the turbulence generators. The external geometry of the turbulence generators used according to the invention is strongly dictated by the geometry of the burner channel. In the case of circular channels recommended as described, the cylindrical shape, in the case of a rectangular cross-section of the burner channel is preferably a cuboid body. The respectively particularly suitable embodiment can be determined by a person skilled in the art.

The diameters of the bores to be mounted in the turbulence generators are usually from 0.1 to 0.5, preferably from 0.2 to 0.4, times the diameter of the cylinder, i. the outer diameter of the turbulence generator.

The gas undergoes the above-described deflection in the inventive method when flowing through the holes in the turbulence generators. Thus, the gas is given a twist, it forms a twisted flow. Thus, the deflection of the flowing medium generates a pronounced radial and tangential velocity component at the outlet from the burner. Due to the high shear forces exerted by neighboring emerging beams (ie, from adjacent burner channels), high fluctuation velocities occur , This can be advantageously generated in the combustion chamber, the formation of an energetically high-intensity, turbulent flow field in which the reaction zone can form. The turbulence formed is characterized by flow conditions in which high fluctuation velocities are formed in all three spatial directions and, furthermore, no macroscopic preference in the circumferential direction can be recognized.

The inventive arrangement of the turbulence generators in the channels of the burner block results in a new and improved process management, which will be discussed in more detail below. According to the invention, another type of stabilization of the reaction takes place here. In addition to the use of holding flames, the turbulence generator generates a high-intensity flow field in which the reaction zone can form. The nature of the formed flow field and the process control advantageously causes no recirculation of streams near the burner block to be observed here, which ultimately leads to no coke deposits being observed on the burner block. In addition to the already described advantageous embodiment of the turbulence field, the avoidance of undesirable recirculation of gas streams containing Russian to the burner block is also effected by the inventive design of the positioning of the holding flame. The holding flames are in contrast to conventional burners at a significant distance from the burner block, preferably the distance is 3 to 20, more preferably 4 to 15 times, more preferably 6 to 15 times the diameter of a channel in the burner block. This distance is measured from the lower edge of the burner block, ie the point at which the gas stream leaves the channels in the direction of the combustion chamber and the point at which the auxiliary oxygen is introduced into the combustion chamber. Usually, the diameters of the channels in the burner block are in a range of 17 to 27 mm, preferably 20 to 23 mm. As a result of this positioning of the holding flames, the flame in the method according to the invention stabilizes far further away from the burner block than in conventional burners. The particular preferred positioning of the holding flame depends on the particular system and the specific predetermined procedural conditions. A corresponding variation can be carried out in a particular case by the skilled person depending on the given reaction conditions. A simple displacement of the holding flames in conventional burners to a similar distance would not be comparable to success, since its burner bores are not provided according to the invention with turbulence generators and thus downstream of the outlet no turbulent flow field, in which the main flame only by inserting auxiliary oxygen and (stabilized) without the stabilizing effect of the recirculations at the burner outlet holes.

The inventive method provides a high turbulence generation in the combustion chamber with minimal pressure loss. The pressure loss depends on the throughput and is at the design point of the reactor at 40 to 300 mbar.

In their arrangement, the turbulence generators preferably have an alternating direction of rotation (clockwise and counterclockwise). As a result, it is advantageously possible to form a turbulent flow field in the combustion chamber without an integral resultant of the tangential velocity, as a result of which a particularly effective mixing can be achieved.

A preferred arrangement of the turbulence generators provides that in the radial direction, the directions of rotation are alternated, in the circumferential direction, however, turbulence generators of the same type are used. The arrangement of directions of rotation for the oxidizer and fuel leading turbulence generators in the burner plate are in FIG FIG. 2 shown.

It can be arranged both in all channels and only in some of them turbulence generators.

Another object of the present invention is a device suitable for carrying out the method according to the invention. This will be described below on the basis of FIG. 1 explained in more detail by way of example.

Means of feeds (1) and (2) are fed to oxidizer and fuel separately from one another by turbulence generator lines (3) in the burner block. Only downstream of the turbulence generators, which are preferably made of axial swirl generators, come oxidizer and fuel in contact and are mixed in the intense turbulence field. Mixing chamber (4) is dimensioned in length so that it is sufficient for a sufficient homogenization of the mixture.

Through the feeds (5), oxygen or a reaction auxiliary enters the reaction space (6), where the reaction zone is stabilized.

In FIG. 2 a preferred arrangement of the turbulence generators is shown. With "R" and "L" schematically Turbulenzgeneratoren different direction of rotation are designated ("R" clockwise, "L" counterclockwise). Accordingly, in the circumferential direction, turbulence generators of the same direction of rotation are preferably located on a circular arc, while alternating directions of rotation are arranged in the radial direction. In the pipes, which in the FIG. 2 marked with hatching, this oxidizer is initiated.

The process of the invention enables an economical partial oxidation of hydrocarbons. It is particularly suitable for the production of

Acetylene and synthesis gas in high yields. In contrast to methods in conventional burners, the process provides for partial oxidation without undesirable coke deposition which leads to an impairment of the process. Here, the inventive method of stabilizing the flame in the burner opens due to the avoidance of coke deposition by recirculation an effective and economical reaction. Here, the advantages can be realized in a simple manner by the fluidic design according to the invention, an increased effort such as the periodic mechanical cleaning of the burner can be avoided.

example

Experimental measurements were made of the mixture in accordance with the FIG. 1 shown, device according to the invention carried out. A reactor room with a diameter of 170mm was provided with 37 holes of 25mm. The gas leaving the holes was considered by the turbulence generators contained in the lines at the flow outlet of the holes with a tangential velocity component with alternating direction of rotation.

The turbulence generators were characterized by four holes, which covered an angle of 360 ° with a length of the cylinder of 5 cm.

The distribution of the oxidizer and fuel admission was chosen so that overall results in a uniformly distributed pulse current density from the respective holes, this was an arrangement as in FIG. 2 is shown selected.

Radial concentration measurements were carried out to determine the quality of the mixture of oxidizer and fuel at the level of flame stabilization, ie at the outlet of the mixing section and transition into the reactor space. The distance between the measuring point and the outlet of the reaction media (designation 7 in FIG. 1 ) was 8 bore diameter. In the diagram in FIG. 3 the determined mixing quality is shown by radial position (determined over the entire reactor diameter of 170 mm). The diagram shows the percentage deviation of the actually determined mixture in terms of the fuel content (methane) compared to an ideal mixture. It should be noted that the deviation from the ideal mixing in the embodiment according to the invention is less than 1 percent, thus this embodiment opens up an effective method implementation.

Claims (8)

1. A process for partial oxidation of hydrocarbons in a reactor, in which a stream comprising the hydrocarbon and a stream comprising the oxygen are fed to the reactor, wherein both streams fed to the reactor are conducted within the reactor separately through in each case one or more spatially separate lines, these lines having turbulence generators in their interior, owing to which, as a result of the imposed deflection of the flow direction downstream of said turbulence generators, a highly turbulent flow field forms, the turbulence generators blocking 10 to 70% of the percentage area of the flow cross section and the streams conducted through the turbulence generators, as they flow through, undergoing curved deflection in a circumference angle of from 45° to 360°, and the streams then having a tangential flow component after exiting from the lines and being mixed in a mixing zone and then converted in a reaction zone.
2. The process according to claim 1, wherein acetylene and synthesis gas are prepared by partial thermal oxidation.
3. The process according to claim 1 or 2, wherein turbulence generators are used in all lines.
4. The process according to claims 1 to 3, wherein the turbulence generators are disposed in the lines such that, as the stream flows through the channels, based on adjacent channels, an alternating direction of rotation is formed.
5. The process according to claims 1 to 4, wherein a suitable mixture of reactants is formed by disposing the stabilizing flame at a distance of from 6 times to 15 times the channel diameter from the lower edge of the burner block measured in the burner space.
6. An apparatus for performing the process according to claims 1 to 5 which comprises a reactor for acetylene preparation, said reactor comprising, based on the flow direction of the feed stocks upstream of the mixing zone of the feed stocks, separate lines in which, spatially separately, the stream comprising the hydrocarbon and the stream comprising the oxygen are conducted, the interior of one or more of these lines comprising turbulence generators, the turbulence generators blocking 10 to 70% of the percentage area of the flow cross section and the streams conducted through the turbulence generators, as they flow through, undergoing curved deflection in a circumference angle of from 45° to 360°, and the ends of these lines opening into the mixing zone in which the feed stocks added are mixed and reacted.
7. The apparatus according to claim 6, wherein the turbulence generators arranged in the line(s) block the line cross section to an extent of from 10% to 70%.
8. The apparatus according to claim 6 or 7, wherein the turbulence generator(s) has/have bores for the passage of a stream and these bores are arranged with a slope of from 40° to 80° based on the longitudinal axis of the line.

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